The invention relates to an arrangement for controlling the oil feed into a control chamber of a piston with variable compression height, particularly for internal-combustion engines, which control chamber is arranged between an interior piston part coupled to a connecting rod and an exterior piston part that is slidably guided at the interior part, and which control chamber is connected to the lubricating oil circuit of the internal-combustion engine, via an oil feed system which includes a longitudinal oil bore through the connecting rod shaft. A control valve is disposed in the longitudinal oil bore to control oil flow therethrough.
In the case of a known arrangement of the above-mentioned type (DE-PS No. 17 51 703), the control valve is developed within the longitudinal bore of the connecting rod as a simple check valve that, as a result of its mass, when the accelerating forces act in the direction of the crankshaft, closes an inflow bore. As a result, it is avoided that, particularly in the BDC-range of the piston, the oil column that is located above the valve, because of its inertial force directed at the crankshaft, can flow off in the direction of the connecting rod bearing. However, the check valve cannot prevent that, when the internal-combustion engine is stopped, because of leakages, oil escapes from the control chamber of the piston and as a result, the compression height at the piston is reduced, which results in a deterioration of the cold start behavior of the internal-combustion engine.
It is therefore an objective of the invention to improve the known check valve in such a way that, particularly during a cold start, the piston, within a short period of time, can be adjusted to its maximum compression height.
According to the invention, this objective is achieved by providing that the control valve has slidable automatically opening additional oil supply bore feed openings during engine starting operation.
By means of the invention, it is achieved that the check valve, in addition to its previous blocking function, can be used also for the control of the oil volume from the lubricating oil circuit into the control chamber of the piston.
By means of the arrangement of an additional control bore in the valve, which is opened only in the starting phase, an additional amount of oil is controlled into the control chamber for a short time, by means of which a rapid upward control of the piston into the position of the maximum compression height is achieved. The resulting increase of the compression pressure in the combustion chamber improves the starting of the engine, particularly during a cold start.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.